Spray guns for applying paint to a surface are well known. Examples of spray guns and associated spray equipment can be found in the following patents:
U.S. Pat. No. 3,463,395 to Binoche PA1 U.S. Pat. No. 4,848,665 to Smith PA1 U.S. Pat. No. 2,029,423 to Gustafsson PA1 U.S. Pat. No. 3,746,253 to Walberg PA1 U.S. Pat. No. 2,867,476 to Siefen PA1 U.S. Pat. No. 4,844,347 to Konhauser et al. PA1 U.S. Pat. No. 4,154,403 to Forrester PA1 U.S. Pat. No. 3,841,555 to Lilja PA1 U.S. Pat. No. 4,844,342 to Foley PA1 U.S. Pat. No. 3,658,255 to Beall, Jr. PA1 a central nozzle having an orifice for supplying said liquid to be atomized; PA1 a cap having a funnel shaped chamber mountable over said nozzle to define an annular passage for supplying said pressurized gas; PA1 said cap having an orifice alignable with said nozzle orifice such that said nozzle orifice is recessed upstream from said cap orifice to define a region adjacent said nozzle orifice in which said liquid is atomized by said pressurized gas into a liquid spray prior to being expelled through said cap orifice.
In recent years, high volume low pressure (HVLP) spray gun systems have become popular as they offer better transfer efficiency and a good quality finish on surfaces. Examples of patents covering HVLP spray gun systems are found in U.S. Pat. Nos. 4,905,905, 4,915,303 and 4,948,053.
An important feature of HVLP systems is that use of low pressure air (in the range of 0-20 psi) makes it easier to control the spray pattern created by the spray gun. In older high pressure spray systems, the high pressure air used tends to create an uncontrolled fogging spray cloud due to the fact that the high pressure air expands rapidly on leaving the spray gun. Rapid expansion of the spray results in as little as 30 per cent of the paint atomized being delivered to the surface to be painted.
Besides wasting expensive paint, high pressure air systems or any other spray system that creates a large cloud of atomized particles is a potential health hazard. In the United States, a number of states have enacted legislation to protect the environment from harmful Volatile Organic Compounds. This new legislation requires a spray transfer efficiency of approximately 65%. Since high pressure systems tend to deliver only 25 to 30% transfer efficiency and some HVLP systems begin at a transfer efficiency of 65%, it is easy to see why HVLP systems have become so popular.
HVLP systems presently in use can be improved upon. Low pressure air is not normally as efficient at atomizing the liquid to be sprayed. In general, if the atomization of the paint is improved, the surface quality of the resulting paint job is also improved.